1. Field of the Invention
The present invention relates to a motor drive control circuit of a position-sensorless type, and to a motor drive apparatus provided with such a motor drive control circuit.
2. Description of the Prior Art
In conventional position-sensorless motor drive control circuits, one way to start a motor is by forcibly vibrating the motor with a predetermined sequence that is unrelated to the position of the rotor (hereinafter refereed to as “Method I”). Another way is by providing a current detection resistor and feeding the stator coils of the motor with current pulses before starting the motor so as to detect the energization status of the stator coils with the current detection resistor and then determine, according to the result of the detection, the starting logic state that permits the motor to be started in the forward direction (hereinafter refereed to as “Method II”).
FIG. 11 shows an example of the configuration of a position-sensorless motor drive apparatus that starts a motor by Method II described above. A drive portion 1 converts a drive voltage VD into three-phase voltages, and outputs them to a three-phase brushless motor 2 (hereinafter referred to as the motor 2). A current detection resistor R5 detects the energization status of the drive portion 1. A motor drive control circuit 3′ detects the current that flows through the current detection resistor R5 before the motor 2 is started, then determines, according to the detected current, the starting logic state that permits the motor to be started in the forward direction, and then controls the drive portion 1 with drive signals generated on the basis of the starting logic state.
However, Method I described above has the disadvantage that, since the motor is fed with three-phase voltages generated on the basis of a starting logic state that is unrelated to the rotor position, the motor is not always started in the forward direction. On the other hand, Method II has the disadvantage that the current detection resistor produces a power loss. Thus, there have conventionally been available no motor derive apparatuses that are suitable for use in portable appliances, such as portable MD (minidisk) players, in which rotation of a disk is frequently started and stopped.
Incidentally, in the motor drive apparatus disclosed in Japanese Patent Application Laid-Open No. H5-268791, the rotor position is detected by monitoring zero-cross voltages in coils that are in a floating state. With this detection method, however, it is not possible to detect the rotor position unless the motor is rotating. Thus, with this detection method, it is possible to detect the rotor position when synchronism is recovered after being momentarily lost, but it is impossible to detect the rotor position before the starting of the motor.